1``for``
2=======
3
4Loop over each item in a sequence. For example, to display a list of users
5provided in a variable called ``users``:
6
7.. code-block:: jinja
8
9    <h1>Members</h1>
10    <ul>
11        {% for user in users %}
12            <li>{{ user.username|e }}</li>
13        {% endfor %}
14    </ul>
15
16.. note::
17
18    A sequence can be either an array or an object implementing the
19    ``Traversable`` interface.
20
21If you do need to iterate over a sequence of numbers, you can use the ``..``
22operator:
23
24.. code-block:: jinja
25
26    {% for i in 0..10 %}
27        * {{ i }}
28    {% endfor %}
29
30The above snippet of code would print all numbers from 0 to 10.
31
32It can be also useful with letters:
33
34.. code-block:: jinja
35
36    {% for letter in 'a'..'z' %}
37        * {{ letter }}
38    {% endfor %}
39
40The ``..`` operator can take any expression at both sides:
41
42.. code-block:: jinja
43
44    {% for letter in 'a'|upper..'z'|upper %}
45        * {{ letter }}
46    {% endfor %}
47
48.. tip:
49
50    If you need a step different from 1, you can use the ``range`` function
51    instead.
52
53The `loop` variable
54-------------------
55
56Inside of a ``for`` loop block you can access some special variables:
57
58===================== =============================================================
59Variable              Description
60===================== =============================================================
61``loop.index``        The current iteration of the loop. (1 indexed)
62``loop.index0``       The current iteration of the loop. (0 indexed)
63``loop.revindex``     The number of iterations from the end of the loop (1 indexed)
64``loop.revindex0``    The number of iterations from the end of the loop (0 indexed)
65``loop.first``        True if first iteration
66``loop.last``         True if last iteration
67``loop.length``       The number of items in the sequence
68``loop.parent``       The parent context
69===================== =============================================================
70
71.. code-block:: jinja
72
73    {% for user in users %}
74        {{ loop.index }} - {{ user.username }}
75    {% endfor %}
76
77.. note::
78
79    The ``loop.length``, ``loop.revindex``, ``loop.revindex0``, and
80    ``loop.last`` variables are only available for PHP arrays, or objects that
81    implement the ``Countable`` interface. They are also not available when
82    looping with a condition.
83
84.. versionadded:: 1.2
85    The ``if`` modifier support has been added in Twig 1.2.
86
87Adding a condition
88------------------
89
90Unlike in PHP, it's not possible to ``break`` or ``continue`` in a loop. You
91can however filter the sequence during iteration which allows you to skip
92items. The following example skips all the users which are not active:
93
94.. code-block:: jinja
95
96    <ul>
97        {% for user in users if user.active %}
98            <li>{{ user.username|e }}</li>
99        {% endfor %}
100    </ul>
101
102The advantage is that the special loop variable will count correctly thus not
103counting the users not iterated over. Keep in mind that properties like
104``loop.last`` will not be defined when using loop conditions.
105
106.. note::
107
108    Using the ``loop`` variable within the condition is not recommended as it
109    will probably not be doing what you expect it to. For instance, adding a
110    condition like ``loop.index > 4`` won't work as the index is only
111    incremented when the condition is true (so the condition will never
112    match).
113
114The `else` Clause
115-----------------
116
117If no iteration took place because the sequence was empty, you can render a
118replacement block by using ``else``:
119
120.. code-block:: jinja
121
122    <ul>
123        {% for user in users %}
124            <li>{{ user.username|e }}</li>
125        {% else %}
126            <li><em>no user found</em></li>
127        {% endfor %}
128    </ul>
129
130Iterating over Keys
131-------------------
132
133By default, a loop iterates over the values of the sequence. You can iterate
134on keys by using the ``keys`` filter:
135
136.. code-block:: jinja
137
138    <h1>Members</h1>
139    <ul>
140        {% for key in users|keys %}
141            <li>{{ key }}</li>
142        {% endfor %}
143    </ul>
144
145Iterating over Keys and Values
146------------------------------
147
148You can also access both keys and values:
149
150.. code-block:: jinja
151
152    <h1>Members</h1>
153    <ul>
154        {% for key, user in users %}
155            <li>{{ key }}: {{ user.username|e }}</li>
156        {% endfor %}
157    </ul>
158
159Iterating over a Subset
160-----------------------
161
162You might want to iterate over a subset of values. This can be achieved using
163the :doc:`slice <../filters/slice>` filter:
164
165.. code-block:: jinja
166
167    <h1>Top Ten Members</h1>
168    <ul>
169        {% for user in users|slice(0, 10) %}
170            <li>{{ user.username|e }}</li>
171        {% endfor %}
172    </ul>
173